A comparison of dietary methods in nutritional studies.

Dietary intakes of 40 lactating women were measured by a 7-day record (7DR) and compared with results using a 1-day record (1DR), 3-day record (3DR), and a newly developed food frequency form. The estimated intakes of energy, protein, calcium, phosphorus, and iron were used in the comparison. The subjects ranged from 3 wk to 6 months postpartum and all were totally breast-feeding their infants at the time of the study. The 7DR was recorded by the subjects and random days were chosen to provide 1DR and 3DR. The food frequency form is a method developed to estimate nutrient intakes based on the consumption of 105 food items. Intraclass correlation coefficients used to compare methods indicated good, moderate, and poor agreement for 3DR/7DR, 1DR/7DR, and food frequency form/7DR comparisons, respectively. Regression analysis was used to assess further the agreement between 3DR and 7DR. This analysis indicated that the 3DR cannot provide good individual estimates of nutrient intakes, but can provide a reasonable estimate of the general quality of the diet. Intakes also were classified as high (greater than 1 1/3 Recommended Daily Allowance), medium (2/3 to 1 1/3 Recommended Daily Allowance), or low (less than 2/3 Recommended Daily Allowance), and Cohen's kappa was used to measure agreement between methods. None of the intakes was found to agree with the 7DR classification. Intraindividual variation was found to be greater than interindividual variation.